Single or multiple electric actuators frequently use a method and are arranged in a system with a microprocessor based controller that controls electrical current supplied to the electric actuator(s) to control extension and retraction of the actuator(s). The term “electric actuator” means electro-hydraulic actuator and/or electro-mechanical actuator. The term “electro-hydraulic actuator” means a self-contained actuator that converts electrical energy to hydraulic energy and applies the hydraulic energy to cause motion. A typical electro-hydraulic actuator, for example, includes an electric motor that drives a hydraulic pump to pressurize fluid from a reservoir and supply the pressurized fluid to a hydraulic cylinder or other hydraulic motor to cause motion. The term “electro-mechanical actuator” means a self-contained actuator that converts electrical energy to mechanical energy to cause motion. A typical electro-mechanical actuator, for example, includes an electric motor that drives a mechanical rod through a mechanism such as a screw thread to cause motion.
Such methods and systems are used with a wide range of stationary and mobile objects to set and hold the object in a predetermined attitude. The term “attitude” means the orientation or inclination of the axes of the object relative to a plane such as, for example, a horizontal plane or vertical plane. The term “level attitude” means the orientation of the axes of the object in a plane substantially parallel to a horizontal plane.
One example of such method and system is a leveling method and system used with motorized or towed recreational vehicles. Generally, when recreational vehicles are to be parked for an extended period of time, a set of leveling electric actuators is utilized to level and support the vehicle. Once the recreational vehicle is driven to the location where it will be parked, such as, for example, a campground or sporting event, the leveling electric actuators are engaged to position and support the vehicle in a generally level attitude.
In control methods and systems used with single or multiple electric actuators, a technical problem is presented if only some of the electric actuators make ground contact. For example, recreational vehicle or other object leveling systems that use multiple electric actuators to position a vehicle or other object in a level attitude can level the object with only some of the actuators making ground contact. This may occur, for example, if one side of the recreation vehicle is lower relative to ground than the other side of the vehicle. In this example, the electric actuators on the lower side may be extended to lift the lower side and achieve a level attitude for the vehicle while the actuators on the higher side are not making ground contact. If this occurs, even if the vehicle is in a level attitude, the vehicle may sway in a side-to-side direction or shift in a front-to-back direction due to the movement of occupants inside the vehicle or due to wind or other causes.
To address this problem, various methods and systems are disclosed in U.S. Pat. No. 5,143,386, which shows multiple electric actuators mounted on a vehicle to be leveled, an electric controller for extending and retracting the actuators, and electrical current sensors to determine when each actuator is lifting a minimum load. The methods and systems of the general type shown in U.S. Pat. No. 5,143,386 bring the electric actuators to a stop during extension when two conditions are met. These conditions are that each actuator is lifting a minimum load as determined by a preset minimum actuator current draw and that the vehicle has reached a level position as determined by a level sensor. Similar methods and systems of measuring actuator current draw to sense a fully retracted condition may also be used.
A technical problem with respect to sensing ground contact or sensing fully retracted condition or other conditions by measuring current draw is presented by variables in actuator current draw that may not be associated with expected changes in current draw associated with ground contact or full retraction or other desired conditions. For example, while actuators in a system and method may be substantially identical, each will have a different current draw from the other during extension both before ground contact and after ground contact. Also, each individual actuator will itself have variations in current draw from one actuation to another actuation of the same actuator. Further, each actuator will have variations in current drag from one actuation temperature to another and from one actuation duration time to another.